Re: [PATCH v1 05/13] xen/arm: allocate shared memory from heap when host address not provided

[Julien Grall <julien@xxxxxxx>]

Hi Penny,

On 09/01/2023 07:50, Penny Zheng wrote:
> > -----Original Message-----
> > From: Julien Grall <julien@xxxxxxx>
> > Sent: Sunday, January 8, 2023 8:23 PM
> > To: Penny Zheng <Penny.Zheng@xxxxxxx>; xen-devel@xxxxxxxxxxxxxxxxxxxx
> > Cc: Wei Chen <Wei.Chen@xxxxxxx>; Stefano Stabellini
> > <sstabellini@xxxxxxxxxx>; Bertrand Marquis <Bertrand.Marquis@xxxxxxx>;
> > Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
> > Subject: Re: [PATCH v1 05/13] xen/arm: allocate shared memory from heap
> > when host address not provided
> >
> > Hi Penny,
> Hi Julien,
>
> > On 15/11/2022 02:52, Penny Zheng wrote:
> > > when host address is not provided in "xen,shared-mem", we let Xen
> > > allocate requested shared memory from heap, and once the shared
> > memory
> > > is allocated, it will be marked as static(PGC_static), which means
> > > that it will be reserved as static memory, and will not go back to heap even
> > on freeing.
> >
> > Please don't move pages from the {xen,dom}heap to the static heap. If you
> > need to keep the pages for longer, then get an extra reference so they will
> > not be released.
> >
> > > Signed-off-by: Penny Zheng <penny.zheng@xxxxxxx>
> > > ---
> > >    xen/arch/arm/domain_build.c | 83
> > ++++++++++++++++++++++++++++++++++++-
> > >    1 file changed, 82 insertions(+), 1 deletion(-)
> > >
> > > +static int __init allocate_shared_memory(struct shm_membank
> > *shm_membank,
> > > +                                         paddr_t psize) {
> > > +    struct meminfo *banks;
> > > +    int ret;
> > > +
> > > +    BUG_ON(shm_membank->mem.banks.meminfo != NULL);
> > > +
> > > +    banks = xmalloc_bytes(sizeof(struct meminfo));
> > Where is this freed?
> These kinds of info will be only used in boot-time, so maybe I shall
> free them in init_done()?
I don't think you can free it in init_done() because we don't keep a 
pointer to kinfo past construct_dom*().
> Or just after process_shm() ?
This might work. But I think it would be better to avoid the dynamic 
memory allocation if we can.
Cheers,

--
Julien Grall